1. Field of the Invention
The present invention relates to a vehicle brake fluid pressure control apparatus including: a fluid pressure adjusting unit capable of performing adjustment of individually increasing and decreasing brake fluid pressures acting respectively on wheel brakes for front wheels and wheel brakes for rear wheels so as to prevent the front wheels and the rear wheels from being locked during braking; and allowable differential pressure setting means for setting allowable differential pressures allowable between the brake fluid pressures of the wheel brakes for the left and right coaxial front wheels and between the brake fluid pressures of the wheel brakes for the left and right coaxial rear wheels, the operation of the fluid pressure adjusting unit being controlled in such a way that each of the differential pressures between the brake fluid pressures of the wheel brakes for the left and right coaxial front wheels and between the brake fluid pressures of the wheel brakes for the left and right coaxial rear wheels is equal to or lower than a corresponding one of the allowable differential pressures set by the allowable differential pressure setting means.
2. Description of the Related Art
A vehicle brake fluid pressure control apparatus configured to perform anti-lock brake control independently for wheel brakes for left and right coaxial front wheels and left and right coaxial rear wheels is known from Japanese Patent Application Laid-open No. 2007-55583. In this apparatus, an allowable differential pressure selected from allowable differential pressures calculated from a vehicle speed, a lateral acceleration, and fluid pressures of the wheel brakes of the coaxial wheels is set by allowable differential pressure setting means, and a differential pressure larger than the selected differential pressure is prevented from occurring between the brake fluid pressures of the left and right wheel brakes.
Incidentally, in a stable running state where a vehicle is running on a road surface having a high friction coefficient and having no large difference between friction coefficients of the contact road surfaces of left and right wheels, the allowable differential pressures between the brake fluid pressures of the wheel brakes for the left and right coaxial front wheels and the left and right coaxial rear wheels can be set large. However, in the apparatus disclosed in Japanese Patent Application Laid-open No. 2007-55583 described above, when each allowable differential pressure is set, the fluid pressure of the wheel brake of the wheel coaxial with the wheel being a control target is used as a component corresponding to the friction coefficient of the road surface. Hence, it cannot be said that the judgment accuracy of the road surface friction coefficient is excellent. Accordingly, the apparatus has such a problem that the apparatus cannot accurately judge that the vehicle is running on a road surface having a high friction coefficient upon setting the allowable differential pressures and thereby cannot set the allowable differential pressures to sufficiently large values.